Fire-Retardant Oriented Strand Board (OSB)

ABSTRACT

A two-part flame-retardant, a flame-retardant oriented strand (OSB) and method for forming a flame-retardant OSB is provided. The two-part flame-retardant composition includes an aqueous solution containing a water-soluble flame-retardant and a flame-retardant powder that is incorporated into an oriented strand board without substantially affecting the mechanical properties of the oriented strand board. The method includes applying the aqueous solution containing a water-soluble flame-retardant to an oriented strand board furnish and applying a flame-retardant powder to the wetted furnish, without requiring an additional drying step.

BACKGROUND

Oriented strand board, or OSB, is an engineered wood that has beenpopular in many industries due to its low cost and good mechanicalproperties. OSB exhibits excellent strength and durability properties,making it highly desirable for load-bearing applications. OSB can bemanufactured by a similar method to particle board, such as, by addingadhesives and wax to wood strands or flakes, and then compressing themixture in specific orientations, making the OSB easy to produce.

However, while OSB is valued for its low cost and good mechanicalproperties, OSB is inherently flammable, limiting the applications forwhich it may be used. For example, when tested according to ASTM E84,untreated OSB exhibits a Flame Spread Rating of around 150, placinguntreated OSB into Class III for flammability. As such, OSB is generallyunable to be used in applications that specify low flammabilitymaterials, such as wall, floor, and roof sheathing.

Due to OSB's inherent flammability, many efforts have been made toimpart flame-retardance/resistance into the OSB. However, due to theprocess of making OSB, and the need for adhesives and waxes, theattempts have been unsuccessful. Particularly, early attempts tried toincorporate flame-retardant compounds in powdered form into the mixture,either prior to, or during, the introduction of the wax and/or adhesiveto the strands. However, it was quickly found that if enough powderedflame-retardant compounds were introduced into the mixture to impactflammability, the mechanical properties of the OSB were negativelyaffected. Furthermore, the application of flame-retardant compounds inpowdered form brings problems with their uneven distribution in thewooden composite, due to insufficient homogenization between woodenparticles in the mixing drum, as well as settling of powders added tostrands and dusting problems negatively affecting the machinery and OSBmechanical and fire-retardance properties.

There were also attempts to impart flame-retardance/resistance to OSB byusing aqueous solutions containing flame-retardant compounds. However,known flame-retardant compounds were generally insoluble or sparinglysoluble in aqueous solutions. This necessitated large amounts of solventto be applied along with any aqueous solutions, requiring the OSBstrands to be dried for a second time after application of theflame-retardant compounds. This caused many problems in the OSBindustry, as the existing processing capabilities were not equipped fora second drying step after incorporation of the wax and/or adhesive.Furthermore, it was found that many of the water-soluble flame-retardantcompounds, such as ammonium phosphate, degraded the wood over time,particularly at elevated temperatures.

Moreover, attempts were made to introduce flame-retardant compounds asan organic or non-aqueous based solution. However, this greatlyincreased the volatile content of the solution, creating furtherproblems in managing the volatile organic content exposure duringproduction, and amounts of the organic or non-aqueous solutionsremaining in the product. Therefore, the soluble, or sparingly soluble,flame-retardant compounds were also found to be insufficient forimparting flame resistance into the OSB.

Therefore, it would be beneficial to provide a flame-retardant orientedstrand board that overcomes one or more of the above discussed problems.For instance, it would be beneficial to provide a flame-retardantoriented strand board that maintains good mechanical properties whilehaving sufficient flame-retardance/resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features and aspects of the present disclosureand the manner of attaining them will become more apparent, and thedisclosure itself will be better understood by reference to thefollowing description, appended claims and accompanying drawings, where:

FIG. 1 provides a view of a method of forming an oriented strand board;

FIG. 2A illustrates an oriented strand board according to the presentdisclosure;

FIG. 2B illustrates a cross section of an oriented strand boardaccording to FIG. 2A;

FIG. 3 illustrates a cross section of an oriented strand board accordingto FIG. 2A.

Definitions

As used herein, percentages are weight percentages (wt. %) unlessotherwise stated.

As used herein, the terms “about,” “approximately,” or “generally,” whenused to modify a value, indicate that the value can be raised or loweredby 5% and remain within the disclosed embodiment.

As used herein, the terms “flame” and “fire” (e.g. as used in regards toflame-retardant and fire-retardant) can be used interchangeably.

As used herein, the terms “flame-retardant” and “flame-resistant” can beused interchangeably, and refer to a material that has flame-retardantand -resistant properties, or that has been treated to haveflame-retardant and -resistant properties.

As used herein, “flame-retardant powder” may also be termed “micronizedflame-retardant”.

As used herein, the terms “surface layer” and “face layer” can be usedinterchangeably.

As the person of skill in the art will appreciate, 1 pound per squareinch (psi) corresponds to 68.947 millibar (mbar). Accordingly, 50 psicorresponds to 3447.379 mbar, for example.

DETAILED DESCRIPTION

The present inventors surprisingly found a highly effective two-partflame-retardant for oriented strand boards that does not negativelyaffect the mechanical properties of the oriented strand board, and thatdoes not necessitate any additional drying after incorporation of thetwo-part flame-retardant.

Flame-Retardant Compounds and Composition for Oriented Strand Board

Herein provided is a two-part flame-retardant for oriented strand boardcomprising a water-soluble flame-retardant having a solubility in waterof at least about 400 g/L; and a flame-retardant powder.

Water-Soluble Flame-Retardant

The water-soluble flame-retardant has a solubility in water (or anaqueous solution) of at least about 400 grams per liter (g/L), or atleast about 450 g/L, or at least about 500 g/L, or at least about 550g/L or at least about 600 g/L, or at least about 650 g/L, or at leastabout 700 g/L, or at least about 750 g/L, or at least about 800 g/L, orany ranges or values there between.

In some embodiments, the water-soluble flame-retardant is in the form ofa solution, preferably an aqueous solution or a concentrated aqueoussolution.

The solvent for the water-soluble flame-retardant may be an aqueoussolvent, preferably the solvent is water. However, notwithstanding theaqueous solvent, in a further embodiment, an amount of a second solvent,which may be an organic solvent, an anionic solvent, a nonionic solvent,or other solvent used in the art, may be used in addition to the aqueoussolvent. Generally, the second solvent may be used in an amount of about10 wt. % or less, such as about 5 wt. % or less, based upon the totalweight of the solvents. In some embodiments, no organic solvents areused. This minimizes the volatile organic content of the solvent andflame-retardant composition. In some embodiments, only the aqueoussolvent is used.

The water-soluble flame-retardant may be comprised in the two-partflame-retardant of the invention in an amount of at least about 40 wt.%, at least about 45 wt. %, at least about 50 wt. %, at least about 55wt. %, at least about 60 wt. %, at least about 65 wt. %, at least about70 wt. %, at least about 75 wt. %, or at least about 80 wt. %. In someembodiments, the water-soluble flame-retardant may be comprised in thetwo-part flame-retardant of the invention in an amount of about 40 wt. %to about 98 wt. %, or from about 42 wt. % to about 95 wt. %. It shouldbe understood that the above referenced percentages refer to an amountof the water-soluble flame-retardant in their solid form that have beendissolved in the solution.

The water-soluble flame-retardant comprised in the two-partflame-retardant of the invention may be at least one of

-   -   a borate,    -   a borate ester,    -   a borate alkanolamine, preferably a boric acid and aminoethanol        adduct, more preferably a 2-aminoethanol and boric acid adduct,        most preferably a 2:1 wt. % adduct of 2-aminoethanol and boric        acid,    -   an amine phosphoric acid salt, preferably a polyamine phosphoric        acid salt, more preferably a polyethylene amine phosphoric acid        salt, or    -   a dicyandiamide-formaldehyde phosphoric acid salt.

In one embodiment, the water-soluble flame-retardant is selected fromthe group comprising

-   -   a borate,    -   a borate ester,    -   a borate alkanolamine, preferably a boric acid and aminoethanol        adduct, more preferably a 2-aminoethanol and boric acid adduct,        most preferably a 2:1 wt. % adduct of 2-aminoethanol and boric        acid,    -   an amine phosphoric acid salt, preferably a polyamine phosphoric        acid salt, more preferably a polyethylene amine phosphoric acid        salt, or    -   a dicyandiamide-formaldehyde phosphoric acid salt, or    -   combinations thereof.

In one embodiment, the water-soluble flame-retardant is selected fromthe group consisting of a borate,

-   -   a borate ester,    -   a borate alkanolamine, preferably a boric acid and aminoethanol        adduct, more preferably a 2-aminoethanol and boric acid adduct,        most preferably a 2:1 wt. % adduct of 2-aminoethanol and boric        acid,    -   an amine phosphoric acid salt, preferably a polyamine phosphoric        acid salt, more preferably a higher polyethylene amine        phosphoric acid salt,    -   a dicyandiamide-formaldehyde phosphoric acid salt, and    -   combinations thereof.

The borate alkanolamine is preferably a borate alkanolamine adduct,preferably a 2-aminoethanol and boric acid adduct, more preferably a 2:1wt. % adduct of 2-aminoethanol and boric acid.

The amine phosphoric acid salt may be an inorganic phosphate salt formedfrom ammonia, ammonium compounds, or amides and phosphoric acid. Forexample, the amine phosphoric acid salt is formed from amines thatinclude primary, secondary or tertiary amines, diamines, triamines,polyamines, polyethylene amines or combinations thereof.

Polyamines generally refer to polymers having in the chain aminicrepeating units R—NH—R or R—NR—R. Polyethylene amines (also calledpolyalkylenpolyamines or ethyleneamines) are linear, short-chainpolyethyleneimines with a high proportion of primary amino groups withthe general formula H₂[NCH₂—CH₂—NH]_(n)H (with n=2/diethylenetriamine(DETA); n=3/triethylenetetramine (TETA); n=4/tetraethylenepentamine(TEPA), n=5/pentaethylenehexamine (PEHA), n=6/hexaethyleneheptaamine(HEHA)).

Ethyleneamines are defined here as polymeric forms of ethylene diaminewith three or more nitrogen atoms and including piperazine and itsanalogues. A thorough review of ethylene diamine and ethyleneamines canbe found in the Encyclopedia of Chemical Technology, Vol 8, pgs. 74-108.Ethyleneamines encompass a wide range of multifunctional, multireactivecompounds. The molecular structure can be linear, branched, cyclic, orcombinations of these. Examples of commercial ethyleneamines arediethylenetriamine (DETA), piperazine (PIP), triethylenetetramine(TETA), tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA),aminoethylpiperazine (AEP), and aminoethylethanolamine (AEEA). Othercompounds which may be applicable are 1,2-propylenediamine,1,3-diaminopropane, iminobispropylamine,N-(2-aminoethyl)-1,3-propylenediamine,N,N′bis-(3-aminopropyl)-ethylenediamine, dimethylaminopropylamine, andtriethylenediamine.

Suitable polyamines or polyethylene amines include but are not limitedto ethlyenediamine, diethylenetriamine (DETA), triethylenetetraamine(TETA), tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA),hexaethyleneheptaamine, (HEHA), and the like. Ethylene amines of thiskind are referred to herein as “higher ethylene polyamines” orpolyethylene amines. These higher polyethylene amines may exist as ablend or mixture of one or more polyamines.

In one embodiment, the water-soluble flame-retardant comprises adicyandiamide formaldehyde phosphoric acid salt.

In one embodiment, the water-soluble flame-retardant is selected fromthe group comprising of a polyethylene amine phosphoric acid salt, aboric acid and aminoethanol adduct, and combinations thereof.

In one embodiment, the water-soluble flame-retardant comprises apolyethylene amine phosphoric acid salt, a boric acid and aminoethanoladduct or combinations thereof.

In one embodiment, the water-soluble flame-retardant comprises apolyethylene amine phosphoric acid salt.

In a preferred embodiment the water-soluble flame-retardant is selectedfrom the group comprising of a boric acid and aminoethanol adduct, apolyethylene amine phosphoric acid salt, and combinations thereof.

In a more preferred embodiment the water-soluble flame-retardant is apolyethylene amine phosphoric acid salt.

Preferably, the boric acid and aminoethanol adduct is a 2:1 wt. % adductof 2-aminoethanol and boric acid.

Preferably, the polyethylene amine phosphoric acid salt is a reactionproduct of tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA),hexaethyleneheptamine (HEHA), and higher molecular weight polyethyleneamine product such as Polyamine B, or mixtures thereof, with phosphoricacid.

Polyethylene amine products are known to the skilled in the art, and arecommercially available such as Polyamine B (a product by Akzo Nobel, CAS68131-73-7).

The present inventors have surprisingly found that the abovewater-soluble flame-retardants are especially suitable for formingconcentrated aqueous solutions, and surprisingly, exhibit little to nothermal degradation of the OSB, contrary to the shortcomings describedabove in regards to lower molecular weight ammonium phosphates used intwo-part flame-retardants of the prior art.

Flame-Retardant Powder

The flame-retardant powder may have a size on the micrometer scale, e.g.a powder that has been mechanically altered to have particles with amedian size (d50) of from about 1 μm to about 1000 μm, such as fromabout 2 μm to about 850 μm, such as from about 3 μm to about 100 μm,such as from about 20 μm to about 80 μm or any values or ranges therebetween as are known in the art.

Of course, as may be known in the art, “micronized powder” may alsorefer to smaller particle sizes, and thus, may include a portion of theparticles having a size of less than 1 μm. Particularly, the presentdisclosure has found that such a fine particle size allows for an even,uniform coating of the strands or flakes. Furthermore, the remainingsolvent from the water-soluble two-part flame-retardant may allow thefine particles to adhere to the furnish, thus preventing the powder fromsettling to the bottom of the blender or dusting out of the blender.

The solubility of the flame-retardant powder in water or aqueoussolutions is generally lower than that of the water-solubleflame-retardant comprised in the two part flame-retardant of theinvention. For example, the flame-retardant powder has a solubility inwater (or an aqueous solution) of less than about 400 grams per liter(g/L), or less than about 300 g/L, or less than about 250 g/L, or lessthan about 200 g/L, or less than about 150 g/L, or less than about 100g/L.

Additionally or alternatively, and notwithstanding the size of thepowder, the flame-retardant powder may be at least one of

-   -   a boric acid,    -   a borate, such as borax, or disodium octaborate tetrahydrate        (DOT),    -   a phosphorous-nitrogen based powder, for example an        amine-phosphate flame-retardant or a polyamine-phosphate        flame-retardant,    -   ammonium polyphosphate,    -   guanidine phosphate,    -   an adduct of a phosphoric acid and guanidine derivative such as        guanylurea phosphate (GUP), a silicate, or    -   combinations, derivatives, or adducts thereof.

In one embodiment, the flame-retardant powder may be selected from thegroup comprising

-   -   a boric acid,    -   a borate, such as borax, or disodium octaborate tetrahydrate        (DOT),    -   a phosphorous-nitrogen based powder, for example an        amine-phosphate flame-retardant or a polyamine-phosphate        flame-retardant,    -   ammonium polyphosphate (APP),    -   guanidine phosphate,    -   an adduct of a phosphoric acid and guanidine derivative such as        guanylurea phosphate (GUP), a silicate, or    -   combinations, derivatives, or adducts thereof.

In one embodiment, the flame-retardant powder may be selected from thegroup consisting of

-   -   a boric acid,    -   a borate, such as borax, or disodium octaborate tetrahydrate        (DOT),    -   a phosphorous-nitrogen based powder, for example an        amine-phosphate flame-retardant or a polyamine-phosphate        flame-retardant,    -   ammonium polyphosphate (APP),    -   guanidine phosphate,    -   an adduct of a phosphoric acid and guanidine derivative such as        guanylurea phosphate (GUP), a silicate, and    -   combinations, derivatives, or adducts thereof.

In one embodiment, the flame-retardant powder comprises at least one ofan ammonium polyphosphate (APP), or an guanylura phosphate.

In one embodiment, the flame-retardant powder comprises ammoniumpolyphosphate (APP).

Borates suitable as flame-retardant powder are known to the skilledartisan, for example sodium borate (borax), zinc borates, ammoniumfluoroborate [13826-83-0], or barium metaborate.

Ammonium polyphosphates (APP) are known to the skilled in the art, seee.g., ammonium polyphosphate phase 2 (CAS: 68333-79-9).

In one embodiment, the flame-retardant powder comprises at least one of

-   -   a boric acid,    -   a borate, preferably borax or disodium octaborate tetrahydrate        (DOT),    -   an amine-phosphate flame-retardant,    -   an adduct of a phosphoric acid and guanidine derivative,    -   a ammonium polyphosphate (APP),    -   a silicate, or    -   combinations thereof.

In one embodiment, the flame-retardant powder is selected from the groupcomprising

-   -   a boric acid,    -   borax,    -   disodium octaborate tetrahydrate (DOT),    -   guanylurea phosphate (GUP),    -   ammonium polyphosphate (APP), or    -   combinations thereof.

In one embodiment, the flame-retardant powder is selected from the groupconsisting of

-   -   a boric acid,    -   borax,    -   disodium octaborate tetrahydrate (DOT),    -   guanylurea phosphate (GUP),    -   ammonium polyphosphate (APP), and    -   combinations thereof.

In a preferred embodiment, the flame-retardant powder comprises

-   -   a 1:1 blend of boric acid and borax,    -   a 1:1 blend of boric acid and disodium octaborate tetrahydrate        (DOT),    -   guanylurea phosphate (GUP),    -   ammonium polyphosphate (APP), or    -   combinations thereof.

In another preferred embodiment, the flame-retardant powder is selectedfrom the group consisting of

-   -   a 1:1 blend of boric acid and borax,    -   a 1:1 blend of boric acid and disodium octaborate tetrahydrate        (DOT),    -   guanylurea phosphate (GUP),    -   ammonium polyphosphate (APP), and    -   combinations thereof.

In another preferred embodiment, the flame-retardant powder is selectedfrom the group consisting of

-   -   guanylurea phosphate (GUP),    -   ammonium polyphosphate (APP), or    -   combinations thereof.

In a more preferred embodiment, the flame-retardant powder is ammoniumpolyphosphate (APP).

Preferably, said ammonium polyphosphate (APP) is ammonium polyphosphatephase 2 (CAS: 68333-79-9).

The flame-retardant powder may also include an anti-caking additive inconjunction with the flame-retardant powder compound. In someembodiments, the anti-caking additive is a silica, such as a fumedsilica, however, other anti-caking additives may be used as are known inthe art.

Particularly, the present disclosure has found that the flame-retardantpowder can be mixed with the furnish that has been wetted with thewater-soluble flame-retardant to yield an OSB with excellentflame-retardant properties without suffering from the above noteddeficiencies in regards to powder flame-retardants.

The flame-retardant powder may be a “dry powder”, meaning a powdercomprising about 10 wt. % or less of liquid prior to mixing with thewater-soluble flame-retardant. Alternatively, the flame-retardant powdermay be mixed with the water-soluble flame-retardant as a dispersion ofparticles within the aqueous solution comprising the water-solubleflame-retardant.

The water-soluble flame-retardant and the flame-retardant powderaccording to the present invention work together synergistically toprovide excellent flame-retardant properties to the OSB withoutrequiring a large proportion of the OSB by weight to be occupied byflame-retardants.

The two parts of the two-part flame-retardant may be applied together orseparately. Thus, the two parts of the two-part flame-retardant of theinvention may be in the form of a kit comprising the water-solubleflame-retardant and the flame-retardant powder separately, wherein thewater-soluble flame-retardant may be in the form of a solid, or in theform of a solution, preferably in the form of an aqueous solution, orconcentrated aqueous solution, while the flame-retardant powder may bein the form of a solid, or in the form of an aqueous dispersion.Alternatively, the two-part flame-retardant composition of the inventionmay be in the form of a dispersion, wherein the flame-retardant powderis dispersed in the solution of the water-soluble flame-retardant.

In one embodiment, the water-soluble retardant and the flame-retardantpowder forming the two-part flame-retardant of the invention areprovided separately, wherein the water-soluble retardant is in the formof an aqueous solution comprising at least about 40 wt. % of the saiddissolved therein; and wherein the flame-retardant powder is in the formof a solid and has a median particle size (d50) of from about 1 μm toabout 1000 μm.

In one embodiment, the water-soluble retardant and the flame-retardantpowder forming the two-part flame-retardant of the invention areprovided in the form of an aqueous dispersion, comprising at least about40 wt. % of the said dissolved therein; and comprising theflame-retardant powder in the form of a solid having a median particlesize (d50) of from about 1 μm to about 1000 μm dispersed therein.

For example, previously it was found that a high loading ofwater-soluble flame-retardants (15%-20 wt. %) was insufficient toprovide adequate flame-retardant properties to the OSB. Similarly, itwas found that to impart sufficient flame-retardance to the OSB usingflame-retardant powders, a high load of greater than 15%-20 wt. % of theflame-retardant powder was needed, which negatively impacted themechanical properties of the OSB.

However, the present disclosure has unexpectedly found that, by usingthe two-part flame-retardant of the invention, a lower amount by weightof the OSB may be efficiently used, and additionally or alternatively,the combination of the water-soluble flame-retardant and flame-retardantpowder lessen, or eliminate, the negative impact on the mechanicalproperties generally exhibited by fire-retardant treated OSB. Thus, theOSB still exhibits excellent fire-retardant properties even when arelatively low amount of flame-retardants are used, and, additionally oralternatively, negative effects on the mechanical properties of the OSBare lessened or eliminated when the blend of flame-retardants of theinvention are utilized. Furthermore, without wishing to be bound bytheory, it is believed that the lower amount of flame-retardantcompounds, in combination with the low levels of aqueous solution thatremain due to the water-soluble flame-retardant compound, minimize manyof the dusting and incorporation problems discussed above in regards tothe prior art powdered flame-retardant compositions.

Flame-Retardant Oriented Strand Board

The present disclosure is further directed to a flame-retardant orientedstrand board that comprises of at least one inner layer and at least oneouter layer. This oriented strand board comprises the two-partflame-retardant of the invention comprising a water-solubleflame-retardant having a solubility in water of at least about 400 g/Las defined above; and a flame-retardant powder as defined above.

The at least one inner layer will typically comprise the water-solubleflame-retardant, while the at least one outer layer will typicallycomprise at least one of the water-soluble flame-retardant and theflame-retardant powder.

In some embodiments, the at least one outer layer comprises a greatertotal amount of two-part flame-retardant than the at least one innerlayer.

In some embodiments, the oriented strand board comprises about 20 wt. %or less of the two-part flame-retardant.

The present disclosure has found that an oriented strand board (OSB) maybe formed so as to have low flame spread while maintaining itsmechanical properties due to a unique two-part flame-retardantcomposition of the invention. In this manner, the present disclosure hasunexpectedly found that the oriented strand board may contain less thanabout 30% by weight, or even less than about 20% by weight, two-partflame-retardant, thus minimizing the effect on the mechanical propertiesof the OSB, while imparting excellent flame retardance properties.

For instance, as may be known in the art, FIG. 1 generally refers to amethod of producing an oriented strand board 100. As shown in FIG. 1,and for illustration only, logs 102 may be placed onto a belt 104 thatwill transfer the logs 102 for further processing. During processing,the logs 102 may be debarked 106, and put through a stranding machine108, that separates the logs 102 into wood strands and flakes e.g. thewood furnish 110, which are then dried. After drying, the furnish 110 isblended with additives 112, such as adhesive(s) and wax(es), such thatthe furnish 110 can be pressed into the shape of an OSB. After blending112, the furnish may be spread into a layer 111, pressed 113, and cut115 to the desired size, forming an OSB 100.

Thus, as shown in FIG. 1, which illustrates a general process forforming an oriented strand board 100, it would be difficult andeconomically unfeasible to introduce additives prior to drying thefurnish, or to modify the line to add an additional drying step afterintroduction of additives. Therefore, as the two-part flame-retardantand/or individual flame-retardants of the prior art are typicallyincorporated into the furnish during the additive step, which occursafter drying, it would be particularly beneficial to provide a two-partflame-retardant that does not require an additional drying step, and/orthat does not negatively affect the processing line or mechanicalproperties of the OSB. This may be achieved with the two-partflame-retardant composition of the invention.

The water-soluble flame-retardant may be applied to the dried furnish110 in the form of an aqueous solution. Due to the high aqueoussolubility of the particular flame-retardant of the invention, it may becomprised in high concentrations in the aqueous solvent, unlike theaqueous solutions discussed in the prior art.

Therefore, the water-soluble flame-retardant of the invention may beapplied to the furnish with a very low amount of solvent, so that about15 wt. % of the furnish or less of the solvent is introduced to thefurnish when the aqueous solution is applied, such as about 12 wt. % ofthe furnish or less, such as about 10 wt. % of the furnish or less, suchas about 8 wt. % of the furnish or less, such as about 7 wt. % of thefurnish or less, or such as about 1 wt. % of the furnish or greater,such as about 3 wt. % of the furnish or greater solvent introduced tothe furnish when the aqueous solution is applied, or any values orranges there between. Thus, the furnish 110 does not need to undergo afurther drying step, as only a small volume of solvent is applied withthe water-soluble flame-retardant.

Moreover, it has been unexpectedly found that a flame-retardant powdermay be used in an amount of from about 20 wt. % or less of the furnish,such as from about 18 wt. % or less, such as from about 15 wt. % orless, such as from about 12 wt. % or less, such as from about 10 wt. %or less, such as from about 8 wt. % or less, such as from about 6 wt. %or less, or such as about 1 wt. % or greater, such as from about 3 wt. %or greater, by weight of the furnish, or any values or ranges therebetween, and exhibit excellent flame-retardant properties while stillyielding an OSB with good mechanical properties.

For instance, in some embodiments, the flame-retardant oriented strandboard of the invention comprises a total amount of both thewater-soluble flame-retardant and the flame-retardant powder from about2 to about 30 wt. %, such as from about 3 to about 25 wt. %, such asfrom 4 to 20 wt. %, such as from 5 to 18 wt. %, such as from 6 to 17 wt.%, such as from 7 to 16 wt. %, such as from 8 to 15.5 wt. %, or anyvalues or ranges there between.

In one embodiment, the flame-retardant oriented strand board of theinvention comprises about 20 wt. % or less of the two-partflame-retardant of the invention. For example, the flame-retardantoriented strand board of the invention comprise from about 2% to about20 wt. %, such as from about 2.5% to about 18%, such as from about 3% toabout 16%, such as from about 3.5% to about 15%, such as from about 4%to about 12%, such as from about 4.5% to about 9 wt. %, or any values orranges there between of the two-part flame-retardant of the invention.

Additionally, or alternatively, additives as known in the OSB art may beincorporated into the furnish. Generally, any additive as known in theart may be used, such as adhesives, waxes, insect repellants, moistureresistant compounds, fungicides, biocides, and color dyes.

Particularly, in some embodiments, one or more adhesives areincorporated into the furnish 110. The adhesives, and other additivesmay be incorporated into the furnish either before, after, or alongwith, the two-part flame-retardant. The adhesive may be a formaldehydeadhesive, an isocyanate adhesive, a melamine or melamine urea adhesive,or combinations thereof. For example, the adhesive may be a polymericmethylene diisocyanate (PMDI), a urea formaldehyde, amelamine-urea-formaldehyde, a phenol formaldehyde, or combinationsthereof. Of course one or more layer(s) of the OSB may include anadhesive that is different from another layer. For instance, an innerlayer may contain a PMDI adhesive, where an outer layer contains adifferent adhesive. However, it is also contemplated that only a singleadhesive is used regardless of the number of layers.

In a further embodiment, waxes are incorporated along with one or moreparts of the two-part flame-retardant. For instance, a wax according tothe present disclosure may be a wax emulsion used to control waterabsorbency and swelling, such as paraffin wax emulsions. Of course,other waxes and wax emulsions may be used as known in the art.

While layers and different compositions of layers have been describedherein, the following disclosure of an OSB and a method of making an OSBaccording to the present disclosure may further describe an aspect orembodiment of the present disclosure that includes an OSB with more thanone layer.

An OSB may generally have at least one inner layer and at least oneouter layer. The inner layer or layers may also be referred to as thecore layer, and the outer layer or layers may be referred to as thesurface layer. For example, the OSB may have at least about one innerlayer, such as at least about two inner layers, such as about threeinner layers, such as about five inner layers or less, such as aboutfour layers inner or less, or any range or value there between.Similarly, the OSB may have at least about one outer layer, such as atleast about two outer layers, such as about three outer layers, such asabout five outer layers or less, such as about four outer layers orless, or any range or value there between. In some embodiments, there isonly one inner layer and one outer layer, and in alternative embodimentsthere is any combination of inner and outer layers as described above.It should be understood that the layers may be assembled or formed suchthat there is no visible distinction between the layers. Therefore, theinner and outer layers may also be in reference to an inner zone and anouter zone of a continuous OSB.

For instance, referring to FIGS. 2A and 2B, an OSB is generally shown inFIG. 2A, and a cross section of FIG. 2A is shown in FIG. 2B. As shown,an oriented strand board 100 may be formed from furnish 110 that hasbeen placed in one or more layers to form a mat, and then pressedtogether to form the OSB. Therefore, the furnish 110 is oriented in oneor more directions in the final product. As described above, the furnish110 may be oriented in a variety of directions as are known in the art.Regardless, in some embodiments, the OSB may have one or more innerlayers 112 and one or more outer layers 114. As described above, itshould be understood that while FIG. 2B is shown as having one innerlayer 112 and one outer layer 114, both the inner layer 112 and outerlayer 114 may contain one or more layers and be inclusively referred toas the inner layer or core layer, and the outer layer may contain one ormore layers and inclusively be referred to as the outer layer or surfacelayer. Thus, it should be understood that both or either of the innerlayer and outer layer of FIG. 2B may contain one or more layers.

As shown in FIG. 2B, the inner layer or core layer 112 may contain oneor more water-soluble flame-retardants 116. As shown in FIG. 2B, the oneor more water-soluble flame-retardants 116 may be generally evenlydispersed throughout the one or more inner layers 112. Of course, itshould be understood that the one or more water-soluble flame-retardants116 may be dispersed in clumps, more localized to the exterior of thelayer, or formed as a gradient increasing in concentration towards theexterior of the layer, depending upon the desired end product and use.In some embodiments, as shown in FIG. 2B, the one or more water-solubleflame-retardants may be dispersed in a substantially continuous andhomogenous manner.

Regardless of the manner of dispersing the at least one water-solubleflame-retardant 116, as shown in FIG. 2B, in some embodiments, the innerlayer 112 may contain little to no flame-retardant powder 118. Forexample, as shown in embodiment of FIG. 2B, the flame-retardant powderis only contained in the outer layer or layers 114. However, it shouldbe understood that the inner layer may contain both the water-solubleflame-retardant 116 and the flame-retardant powder 118 depending on thedesired end product.

Particularly, while the present disclosure has unexpectedly found thatthe combination of the water-soluble flame-retardant and flame-retardantpowder work synergistically to provide an OSB with excellentflame-retardance while maintaining excellent mechanical properties inthe OSB, the present disclosure has also found that the water-solubleflame-retardant may provide excellent protection to the core layer evenwithout the flame-retardant powder, when used in conjunction with asurface layer according to the present disclosure. Therefore, it hasbeen found that the mechanical properties of the OSB according to thepresent disclosure may be further improved, such as by using only awater-soluble flame-retardant in the core layer, in some embodiments, toimprove the strength of the core, while maintaining excellentflame-retardant properties by using a surface layer formed according tothe present disclosure to synergistically yield excellent mechanicalproperties.

In a further embodiment, such as generally shown in FIG. 3, which alsodisplays a cross section of an OSB such as shown in FIG. 2A, the OSB mayhave more than one inner layer 112 and 113 and/or more than one outerlayer 114 and 15. However, it should be understood that the OSB may alsoinclude orientations where there is only one inner layer and two or moreouter layers, or only one outer layer and two or more inner layers.Regardless, as shown in FIG. 3, in some embodiments, the inner layers113 may contain a higher concentration of the water-solubleflame-retardant 116 than inner layer 112. In an alternative embodiment,both inner layers 112 and 113 may have generally the same amount anddistribution of the water-soluble flame-retardant. Nonetheless, as shownin FIG. 3, the inner layers may have a gradient, with the amount byweight of water-soluble flame-retardant 116 used in the OSB increasingin concentration towards the exterior of the OSB.

Regardless of whether the inner layer(s) has one or bothflame-retardants or whether the inner layer is formed from one or morelayers, in some embodiments, the outer layer may include both thewater-soluble flame-retardant 116 and the flame-retardant powder 118. Insuch a manner, the surface layer, which may directly contact a flame,contains both parts of the two-part flame-retardant.

Similarly, as described for the inner layers in FIG. 3, and referringagain to FIG. 3, the outer layer 114 may contain only a small amount byweight of the flame-retardant powder, and a similar amount of thewater-soluble flame-retardant as compared to outer layer 115 which has ahigher amount by weight of the flame-retardant powder 118. In such amanner, the gradient that began in the inner layers may be continued bythe flame-retardant powder 118 in the outer layer(s) 114/115. In someembodiments, the amount of the water-soluble flame-retardant 116 may bethe same or similar in all inner layers 112/113, and the water-solubleflame-retardant 116 and flame-retardant powder 118 may be included inthe same or similar amounts in all outer layers 114/115.

In some embodiments where the inner layer or core layer contains thewater-soluble flame-retardant, the inner layer or core layer may containthe water-soluble flame-retardant in an amount from about 1 to about 10wt. % of the inner layer(s), such as from about 2 to about 9 wt. %, suchas from about 3 to about 8 wt. %, or any ranges or values there between,of the inner layer(s). Of course, it should be understood that if morethan one inner layer is used, both layers individually may have the sameor differing amounts of the water-soluble flame-retardant within theabove recited ranges and may also have an average across all innerlayers within the above recited ranges.

In some embodiments where the outer layer contains both thewater-soluble flame-retardant and the flame-retardant powder, the outerlayer may contain both the water-soluble flame-retardant and theflame-retardant powder in an amount of from about 1 to about 40 wt. % ofthe outer layer(s), such as from about 2 to about 35 wt. %, such as fromabout such as from about 3 to about 30 wt. %, such as about 4 to about25 wt. %, such as from about 5 to about 20 wt. %, such as from about 6to about 18 wt. %, such as from about 7 to about 17 wt. %, or any rangesof values there between, of the outer layer(s). Additionally, similar tothe inner layer(s), it should be understood that if more than one outerlayer is used, both layers individually may have the same or differingamounts of total flame-retardant compounds within the above recitedranges and may also have an average across all outer layers within theabove recited ranges.

Additionally or alternatively, in some embodiments the outer layer maycontain the water-soluble flame-retardant in an amount of from about 1to about 20 wt. % of the outer layer(s), such as from about 2 to about18 wt. %, such as from about 3 to about 15 wt. %, or any ranges orvalues there between, of the outer layer(s). Additionally, as discussed,it should be understood that if more than one outer layer is used, bothlayers individually may have the same or differing amounts of totalflame-retardant within the above recited ranges and may also have anaverage across all outer layers within the above recited ranges.

Similarly, in some embodiments, the outer layer may contain theflame-retardant powder in an amount of from about 1 to about 20 wt. % ofthe outer layer(s), such as from about 2 to about 18 wt. %, such as fromabout 3 to about 15 wt. %, such as from about 4 to about 12 wt. %, suchas from about 5 to about 10 wt. %, or any ranges or values therebetween, of the outer layer(s). Additionally, it should be understoodthat if more than one outer layer is used, both layers individually mayhave the same or differing amounts of total two-part flame-retardantwithin the above recited ranges and may also have an average across allouter layers within the above recited ranges.

Furthermore, in an embodiment where the inner layer or core layercontains the water-soluble flame-retardant, and the outer layer orsurface contains both the water-soluble flame-retardant and theflame-retardant powder, the oriented strand board may have a totalamount of the water-soluble flame-retardant and the flame-retardantpowder of from about 1 to about 30 wt. % of the OSB, such as from about2 to about 27.5 wt. %, such as from about 3 to about 25 wt. %, such asfrom about 4 to about 22.5 wt. %, such as from about 5 to about 20 wt.%, such as from about 6 to about 18 wt. %, or any values or ranges therebetween, of the oriented strand board.

Regardless of the orientation selected, the present disclosure has foundthat the combination of the water-soluble two-part flame-retardant andthe flame-retardant powder compound unexpectedly exhibits synergisticimprovement while exhibiting excellent mechanical properties. Forinstance, when measured using the Schlyter test as described herein, OSBaccording to the present disclosure may exhibit a flame spread incentimeters (cm)*minutes of about 210 cm*minutes or less, such as about200 cm*minutes or less, such as about 190 cm*minutes or less, such asabout 180 cm*minutes or less, such as about 170 cm*minutes or less, suchas about 160 cm*minutes or less, such as about 150 cm*minutes or less,such as about 140 cm*minutes or less, such as about 130 cm*minutes orless, such as about 125 cm*minutes or less, such as about 115 cm*minutesor less, such as about 105 cm*minutes or less, such as about 95cm*minutes or less, such as about 90 cm*minutes or less, or any rangesor values there between. Preferably, the flame-retardant oriented strandboard exhibits an integrated flame height in cm*minutes of about 200 cmor less after 30 minutes.

Similarly, an OSB according to the present disclosure may exhibit aninternal bond strength of about 50 psi or greater, such as about 60 psior greater, such as about 70 psi or greater, such as about 80 psi orgreater, such as about 90 psi or greater, such as about 95 psi orgreater, such as about 225 psi or less, such as about 200 psi or less,such as about 175 psi or less, such as about 150 psi or less, such asabout 125 psi or less, or any ranges or values there between.Preferably, the oriented strand board has an internal bond strength ofabout 50 psi or greater.

Furthermore, an OSB according to the present disclosure may have amodulus of elasticity of about 350,000 psi or greater, such as about400,000 psi or greater, such as about 450,000 psi or greater, such asabout 500,000 psi or greater, such as about 550,000 psi or greater, suchas about 600,000 psi or greater, such as about 650,000 psi or greater,such about 750,000 psi or less, such as about 725,000 psi or less, suchas about 700,000 psi or less, such as about 675,000 psi or less, or anyvalues or ranges there between.

Moreover, an OSB according to the present disclosure may have a modulusof rupture of about 1,750 psi or greater, such as about 2,000 psi orgreater, such as about 2,250 psi or greater, such as about 2,500 orgreater, such as about 4,250 psi or less, such as about 4,000 psi orless, or any ranges or values there between.

In one embodiment, the two-part flame-retardant for oriented strandboard comprises a water-soluble flame-retardant and a flame-retardantpowder, wherein the water water-soluble flame-retardant comprised in thetwo-part flame-retardant of the invention may be at least one of

-   -   a borate,    -   a borate ester,    -   a borate alkanolamine, preferably a boric acid and aminoethanol        adduct, more preferably a 2-aminoethanol and boric acid adduct,        most preferably a 2:1 wt. % adduct of 2-aminoethanol and boric        acid,    -   an amine phosphoric acid salt, preferably a polyamine phosphoric        acid salt, more preferably a polyethylene amine phosphoric acid        salt, or a dicyandiamide-formaldehyde phosphoric acid salt        and wherein the flame-retardant powder may be at least one of    -   a boric acid,    -   a borate, such as borax, or disodium octaborate tetrahydrate        (DOT),    -   a phosphorous-nitrogen based powder, for example an        amine-phosphate flame-retardant or a polyamine-phosphate        flame-retardant, ammonium polyphosphate, guanidine phosphate,    -   an adduct of a phosphoric acid and guanidine derivative such as        guanylurea phosphate (GUP),    -   a silicate, or    -   combinations, derivatives, or adducts thereof.

In one embodiment, the two-part flame-retardant for oriented strandboard comprises a water-soluble flame-retardant and a flame-retardantpowder, wherein the water water-soluble flame-retardant is selected fromthe group comprising

-   -   a borate,    -   a borate ester,    -   a borate alkanolamine, preferably a boric acid and aminoethanol        adduct, more preferably a 2-aminoethanol and boric acid adduct,        most preferably a 2:1 wt. % adduct of 2-aminoethanol and boric        acid,    -   an amine phosphoric acid salt, preferably a polyamine phosphoric        acid salt, more preferably a polyethylene amine phosphoric acid        salt, or a dicyandiamide-formaldehyde phosphoric acid salt        and wherein the flame-retardant powder is selected from the        group comprising    -   a boric acid,    -   a borate, such as borax, or disodium octaborate tetrahydrate        (DOT),    -   a phosphorous-nitrogen based powder, for example an        amine-phosphate flame-retardant or a polyamine-phosphate        flame-retardant, ammonium polyphosphate, guanidine phosphate,    -   an adduct of a phosphoric acid and guanidine derivative such as        guanylurea phosphate (GUP),    -   a silicate, or    -   combinations, derivatives, or adducts thereof.

In one embodiment, the two-part flame-retardant for oriented strandboard comprises a water-soluble flame-retardant and a flame-retardantpowder, wherein the water water-soluble flame-retardant is selected fromthe group comprising

-   -   a borate,    -   a borate ester,    -   a borate alkanolamine, preferably a boric acid and aminoethanol        adduct, more preferably a 2-aminoethanol and boric acid adduct,        most preferably a 2:1 wt. % adduct of 2-aminoethanol and boric        acid,    -   an amine phosphoric acid salt, preferably a polyamine phosphoric        acid salt, more preferably a polyethylene amine phosphoric acid        salt, or a dicyandiamide-formaldehyde phosphoric acid salt        and wherein the flame-retardant powder is selected from the        group comprising    -   a boric acid,    -   a borate, such as borax, or disodium octaborate tetrahydrate        (DOT),    -   a phosphorous-nitrogen based powder, for example an        amine-phosphate flame-retardant or a polyamine-phosphate        flame-retardant,    -   ammonium polyphosphate,    -   guanidine phosphate,    -   an adduct of a phosphoric acid and guanidine derivative such as        guanylurea phosphate (GUP),    -   a silicate, or    -   combinations, derivatives, or adducts thereof, and        wherein the water-soluble flame-retardant has a solubility in        water of at least about 400 g/L.

In one embodiment the two-part flame-retardant for oriented strand boardcomprises a water-soluble flame-retardant and a flame-retardant powder,wherein the water water-soluble flame-retardant is selected from thegroup comprising of a boric acid and aminoethanol adduct, a polyethyleneamine phosphoric acid salt, and combinations thereof, and wherein theflame-retardant powder is selected from the group comprising an ammoniumpolyphosphate (APP), an guanylura phosphate or combinations thereof.

In one embodiment the two-part flame-retardant for oriented strand boardcomprises a water-soluble flame-retardant and a flame-retardant powder,wherein the water water-soluble flame-retardant is selected from thegroup comprising of a boric acid and aminoethanol adduct, a polyethyleneamine phosphoric acid salt, and combinations thereof, and wherein theflame-retardant powder is selected from the group comprising an ammoniumpolyphosphate (APP), an guanylura phosphate or combinations thereof, andwherein the water-soluble flame-retardant has a solubility in water ofat least about 400 g/L.

In a more preferred embodiment, the two-part flame-retardant fororiented strand board comprises a water-soluble flame-retardant and aflame-retardant powder, wherein the water water-soluble flame-retardanta polyethylene amine phosphoric acid salt, and wherein theflame-retardant powder is an ammonium polyphosphate (APP).

In a more preferred embodiment the two-part flame-retardant for orientedstrand board comprises a water-soluble flame-retardant and aflame-retardant powder, wherein the water water-soluble flame-retardanta polyethylene amine phosphoric acid salt, and wherein theflame-retardant powder is an ammonium polyphosphate (APP) and whereinthe water-soluble flame-retardant has a solubility in water of at leastabout 400 g/L.

Method of Forming a Flame-Retardant Oriented Strand Board

Herein provided is a method of forming an oriented strand boardaccording to the present disclosure. The method comprises:

-   -   applying an aqueous solution comprising a water-soluble        flame-retardant present in the aqueous solution in an amount of        40 wt. % or greater to a first furnish; and    -   applying a flame-retardant powder to the first furnish;        wherein the first furnish is configured to form an oriented        strand board without an additional drying step.

In some embodiments, the method may further comprise a second furnish,wherein the first furnish forms at least one outer layer and the secondfurnish forms at least one inner layer. The second furnish may comprisea water-soluble flame-retardant of the invention.

An oriented strand board according to the present disclosure may begenerally formed as described above with reference to FIG. 1.

During the blending of the furnish 110 with any desired additives 112,“the blending step”, a two-part flame-retardant according to the presentdisclosure is incorporated into the blender. One or more blending stepsmay occur. One or more batches of furnish may be placed into a blenderafter debarking and stranding. However, in the present disclosure, abatch of core furnish may be processed separately from a batch ofsurface furnish. In some embodiments, when both the surface and corelayers are treated with both the water-soluble flame-retardant and theflame-retardant powder, the core layers and surface layers may beprocessed in a single batch.

Typically, a batch of core layer furnish is placed into the blender. Thecore layer furnish may then be sprayed or otherwise coated in an aqueoussolution containing the water-soluble flame-retardant. As describedabove, the aqueous solution may be a concentrated solution, and/or maycontain the water-soluble flame-retardant in an amount greater than 40wt. % of the aqueous solution, or any of the other amounts describedabove. As this is a core furnish, the slightly dampened furnish may bemixed with any desired adhesives, waxes, and additional additives, andthen removed from the blender to be arranged for hot-pressing aftercombination with the surface layer. Of course, it should be understoodthat all or a portion of the core layer batch may remain in the blenderfor further surface layer processing, however, a second batch will bedescribed herein for convenience. Additionally or alternatively, thecore layer furnish may also be processed as will be described for thesurface layers, such that the core layer contains both the water-solubleflame-retardant and the flame-retardant powder.

Thus, a second batch of surface furnish, which may be the same ordifferent than the core layer furnish, may be placed into the blender.As with the core layer, the surface layer furnish may be sprayed orotherwise coated in an aqueous solution containing the water-solubleflame-retardant. However, the slightly dampened surface furnish is thenmixed with the flame-retardant powder. After mixing the flame-retardantpowder with the furnish, the furnish may be mixed with any desiredadhesives, waxes, and additional additives, and then removed from theblender to be arranged for hot-pressing after combination with the corelayer.

While the additives have been described as being introduced into theblender after the introduction and blending of the two-partflame-retardant, it should be understood that the additives may beincluded at the same time as one or more of the flame-retardants, priorto the introduction of one or more of the flame-retardants, and/or afterthe introduction of the two-part flame-retardant, as may generally beknown in the art.

After forming the surface layer and the core layer, which may be thesame or different, both the surface layer furnish and the core layerfurnish may be formed into separate mat(s). Accordingly, in someembodiments, at least one of the first furnish and the second furnish isformed into a mat and pressed. The surface layer furnish mat may belocated on at least one exterior facing side of the core furnish mat,such as at least two exterior sides, such as at least three exteriorsides, such as at least four exterior sides, such as at least fiveexterior sides, or where the surface furnish mat(s) completely surroundthe mat(s) of core furnish. Thus, in some embodiments, a mat formed ofthe second furnish may be disposed between at least two mats formed ofthe first furnish. In some embodiments, the mat may be a roughly cubicalor rectangular three-dimensional shape with six sides. However, the matmay be formed into any size or shape as is generally known in the art.Additionally or alternatively, only a single type of layer may be used(e.g., when the core strands are also treated with the flame-retardantpowder). In that case, one or more layers may be used and may form allor a portion of the width and height of the OSB. Nonetheless, regardlessof whether the furnish is core or surface furnish, the furnish may bearranged such that the furnish with the lowest amount by weight totaltwo-part flame-retardant is located at the centermost part of the mat(in one of, or both, the height and width direction). The furnish withthe highest amount by weight total two-part flame-retardant is locatedon one or more of the outermost sides of the OSB.

In some embodiments, the second furnish is a portion of the firstfurnish that is separated from the first furnish after the applying ofthe aqueous solution but prior to the applying of the flame-retardantpowder.

Regardless of the number and type of the layers, after the mats havebeen formed and placed, the treated furnish may be compressed underpressure and temperature as is known in the art to form the orientedstrand boards.

Further provided is a kit comprising a two-part flame-retardant of theinvention, wherein said water-soluble retardant is in the form of anaqueous solution comprising at least about 40 wt. % of the saiddissolved therein; and wherein the flame-retardant powder is in the formof a solid and has a median particle size (d50) of from about 1 μm toabout 1000 μm.

Further provided is the use of a two-part flame-retardant of theinvention for producing a flame-retardant oriented strand board of theinvention as defined herein above.

Furthermore, certain embodiments of the present disclosure may be betterunderstood according to the following examples, which are intended to benon-limiting and exemplary in nature.

Test Methods and Procedures: Fire Performance Evaluation

Schlyter test: a modified Schlyter test was conducted to evaluate fireperformance. The Schlyter test is described by “Fire Test Methods usedin Research at the Forest Products Lab”, Forest Products Lab Report 1443(1959), US Department of Agriculture Forest Service. The modification ofthe methods was that two 30.5 cm×30.5 cm panels are used instead of the30.5 cm×78.75 cm wood panels. The panels are aligned approximately 5 cmapart in a parallel fashion near the bottom of the apparatus immediatelyadjacent to the gas burner. The gas pressure was regulated toapproximately 20 psi, providing a heat from the burner of about 1228btu/hour. The remaining empty spaces in the Schlyter frame were filledwith non-combustible cement board to minimize heat loss and maintain thevertical air flow. The test was conducted for 30 minutes with the panelscontinuously exposed to the flame. The height of the flame (h) wasrecorded every 30 seconds (Δt) and the Integrated Flame Height (IFH), ameasure of flame spread, was calculated using the formula

IFH=cm*min=Σh _(i) *Δt _(i).

Extended Duration Surface Burning Characteristics

Extended Duration Surface Burning Characteristics of Building Materialswas tested according to ASTM E2768 (30 minute Tunnel Test) (2019). Thistest uses the apparatus and procedure of Test Method ASTM E84 with thetotal test period extended to 30 minutes. The OSB samples were tested byplacing the OSB samples in a rectangular tunnel that is 45 cm in widthby 30.5 cm in height and 762 cm long, with two gas burners at one endthat direct a flame onto the surface of the material under controlledairflow. Distance of the flame travel and the rate at which the flamefront advances during the 30-minute exposure determine the calculatedflame spread index (FSI).

Internal Bond Strength

The internal bond strength of the OSB was measured according to ASTMD1037. The top and bottom surface layer of the OSB are bonded to twometal blocks with a hot melt adhesive. Then the two blocks are pulled bya testing machine to find the maximum load that can break the specimen.Internal bond strength=maximum load/area of specimen. The internal bondstrength can be regarded as “cohesion of the panel in the directionperpendicular to the plane of the panel.”

Abbreviations Used Throughout the Examples

-   GUP: guanylurea phosphate-   APP: ammonium polyphosphate (CAS: 68333-19-9)-   PMDI: polymeric methylene diisocyanate-   DOT: disodium octaborate tetrahydrate (Na₂B₈O_(13.)4H₂O)-   MFF: Maximum Flame Front (MFF)-   FSI: Flame Spread Index-   FR: flame-retardant

TABLE 1 abbreviations and concentrations related to examples SampleLabel wt. % flame-retardant solids polyethylene amine phosphate L1 48borate ester L2 82 1:1 boric acid:borax P1 100 1:1 boric acid:DOT⁺ P2100 GUP* P3 100 APP^($) P4 100 *guanylurea phosphate ^($)ammoniumpolyphosphate (CAS: 68333-19-9) ⁺octaborate tetrahydrate (Na₂B₈O₁₃ ·4H₂O)

Borate Ester Used as the Water-Soluble Flame-Retardant in the Examples

The borate ester used as the water-soluble flame-retardant throughoutthe examples is a 2:1 wt. % adduct of boric acid and 2-aminoethanol.

Preparation of Polyethylene Amine Phosphate

The polyethylene amine phosphate used as the flame-retardant powder inall Examples was prepared by blending together 3,287 grams of water and1,686 grams of a mixture of tetraethylenepentamine (TEPA),pentaethylenehexamine (PEHA), hexaethyleneheptamine (HEHA), and highermolecular weight polyethylene amine products, one example of which maybe available as Polyamine B, (for example as sold by Akzo Nobel, CAS68131-73-7) in a 10 liter mixing vessel. 2,597 grams of 75% phosphoricacid was slowly added while cooling the vessel and mixing, over thecourse of two hours. The resulting liquid, which had a viscosity of 70mPa*s, had approximately 48 wt. % flame-retardant and a pH of 6.2.

General Description for the Manufacturing Procedure of Engineered WoodProducts

General Procedure for Treatment of Engineered Wood Products withFire-Retardant

Procedure for core layer: step 1

Procedure for surface layer: step 1 and step 2

In step 1 the dry strands (moisture content 2-5%) are sprayed with aconcentrated aqueous solution of a flame-retardant. The amount of FRsolution sprayed onto the strands is between 4 and 15%, such that theamount of water introduced onto the dry stands does not exceed about 7%by weight. By minimizing the furnish moisture content to below ˜9%, itis possible to hot-press the formed strand mat without re-drying. On theother hand, if moisture content exceeds about 9%, stream pressure canbuild in the panel during hot pressing and the resin will not bindsufficiently to the wood, resulting in voids and de-lamination in thepanel. After a short mixing time, a majority of the flame-retardantsolution is absorbed into the interior of strands, leaving a lightlydampened surface. Strands from this step are suitable for use as a corelayer.

In step 2 the moistened strands from step 1 are blended with aflame-retardant powder. The strands are uniformly dusted and theresidual dampness on the strands from Step 1 ensures that the powderadheres to the strands.

After step 1 (for the core layer) and Steps 1 and 2 (for the outerlayer), a liquid adhesive resin, and optional 1-2% emulsion wax releaseagent are sprayed onto the strands and uniformly blended. Afterwards thetreated strands are formed into a mat so as to create a gradient,whereby strands treated with water-soluble flame-retardant (equippedwith a lower level of fire-retardant) form the core layer, while strandstreated with water soluble flame-retardant and flame-retardant powder(higher overall fire-retardant concentration) form the outer layers.Finally, the mat is conveyed to a press whereby said wood particles arecompressed with sufficient pressure and temperature to cure the bondingresin to form a composite wood product.

Example 1

Southern pine furnish with a moisture content of 4% was screened toremove fines and placed into a drum blender. Flame-retardants wereincorporated into the core layer, the surface layer, or both, as shownin Table 2 below. The furnish was then blended with 3 wt. % of a PMDI(polymeric methylene diisocyanate) resin and 1.5% of a wax emulsion.Forming boxes were used to form mats having three layers, one core layerbetween two surface layers. The mats were pressed at a platentemperature of 204° C. with a pressing cycle of 360 seconds and pressclosure rate of 20 seconds. After pressing, the panels were cooled fortwo days. After two days, the panels were cut into 30.5 cm×30.5 cmsections and allowed to equilibrate under ambient conditions until amoisture content of approximately 10% was achieved.

Furnish southern pine Moisture content  4% Blend 3 wt. % of a PMDI(polymeric methylene diisocyanate) resin and 1.5% of a wax emulsionPressed 204° C., 360 seconds Panels 30.5 cm × 30.5 cm Final moisture 10%content

TABLE 2 Amount of flame-retardant in core layer and surface layer andresults for example 1. Core layer Surface layer polyethylenepolyethylene Integrated Internal amine borate amine borate 1:1 BoricFlame bond phosphate ester phosphate ester acid:Borax 1:1 Boric GUPHeight strength Sample (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) acid:DOT(wt. %) (cm*min) (psi) control 0 0 0 0 0 0 0 442 150 Commercial 0 0 0 00 0 0 429 OSB 1 4.8 4.8 203 2 4.8 4.8 5.4 208 3 4.8 7.2 8.1 193 4 4.84.8 5.4  79 5 4.8 4.8 160 145 6 4.8 4.8 5.4 168 7 4.8 7.2 8.1 203 8 4.84.8 5.4  79 130

As seen in Table 2, the treated samples all exhibited far better flamespread than the untreated sample and commercial OSB.

Example 2

A core layer formed according to the method of Example 1 was treatedwith an aqueous water-soluble flame-retardant of polyethylene aminephosphate (L1) or borate ester (L2), in an amount equal to 4.8% ofactive dry solids, except that a press temperature of 213° C. and presstime of 160 seconds was used. A surface layer was treated with anidentical amount of the water-soluble flame-retardant (4.8% activesolids) plus an additional 5.4% of a powder flame-retardant compound ofa 1:1 blend of boric Acid and Borax, or a 1:1 blend of boric acid anddisodium octaborate tetrahydrate (Na₂B₈O_(13.)4H₂O, DOT), or guanylureaphosphate (GUP) see Table 3. The total flame-retardant loading in thesurface layers was maintained at 10.2 wt. %, while the overall totalpercentage of flame-retardant across all layers was 7.5 wt. %.

Furnish southern pine Moisture content  4% Blend 3 wt. % of a PMDI(polymeric methylene diisocyanate) resin and 1.5% of a wax emulsionPressed 213° C., 160 seconds Panels 30.5 cm × 30.5 cm Final moisture 10%content

TABLE 3 Amount of flame-retardant in core layer and surface layer andresults for example 2. Core layer Surface layer polyethylenepolyethylene Integrated Internal amine borate amine borate 1:1 BoricFlame bond phosphate ester phosphate ester acid:Borax 1:1 Boric GUPHeight strength Sample (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) acid:DOT(wt. %) (cm*min) (psi) 11 4.8 4.8 5.4 168 12 4.8 4.8 5.4  79 130 13 4.84.8 5.4 208 15 4.8 4.8 5.4  79

As shown in Tab. 3 samples formed to include polyethylene aminephosphate and polyethylene amine phosphate+GUP exhibited internal bondstrength only slightly decreased from the control, and the internal bondstrength for both samples is well above the minimum requirement of 50psi (3447 mbar).

Example 3

A Core layer formed according to the method described in example 1except that Aspen furnish was used and pressed at a temperature of 210°C. for 170 seconds. The core layer was treated with a water-solubleflame-retardant compound of polyethylene amine phosphate (L1) or borateester (L2), in an amount equal to 4.8% of active dry solids. However,the surface layer was treated with varying amounts of flame-retardantcompounds according to Table 4.

TABLE 4 Amount of flame-retardant in core layer and surface layer andresults for example 3 Core layer Surface layer polyethylene polyethyleneInternal amine borate amine borate 1:1 Boric 1:1 Boric bond phosphateester phosphate ester acid:Borax acid:DOT strength Sample (wt. %) (wt.%) (wt. %) (wt. %) (wt. %) (wt. %) (psi) control 0 0 0 0 0 0 107 16 4.84.8 5.4  92 19 4.8 7.2 5.4 107 21 4.8 4.8 5.4  92 23 4.8 7.2 5.4  70

As shown in Tab. 4 samples 16, 19, 21, and 23 all exhibited excellentinternal bond strength well above the minimum threshold of 50 psi (3447mbar), and exhibited only a slightly decreased internal bond strength ascompared to the control.

Example 4

A core layer formed according to the method described in example 1except that that a press temperature of 213° C. and a press time of 160seconds was used. The core layer was treated with a water-solubleflame-retardant compound of polyethylene amine phosphate (L1) thenborate ester (L2), followed by one of guanylurea phosphate (P3) orammonium phosphate (P4), in varying amounts as shown in Table 5.

TABLE 5 Amount of flame-retardant in core layer and surface layer andresults for example 4 Core layer Surface layer polyethylene polyethyleneInternal amine borate amine borate bond phosphate ester phosphate esterGUP APP strength Sample (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %)(psi) control 0 0 0 0 0 0 107 28 4.8 7.2 7.2 116 29 4.8 7.2 7.2  75 334.8 7.2 7.2  96 34 4.8 7.2 7.2  66

As shown in Tab. 5 samples 28, 29, 33, and 34 all exhibited internalbond strength above the threshold of 50 psi.

Example 5

Southern Yellow Pine strands were dried to a moisture content of 4%.Strands for the core and surface layers were treated separately in alarge rotary blender. The order of chemical addition was as follows: thewater-soluble flame-retardant was sprayed first, followed by addition ofpowder flame-retardant, then PMDI resin (4%) and finally wax emulsion(1%).

A total of 33 kg of strands was used for each panel, which representedthe combined total of strands forming the respective core and surfacelayers. The strands were layered in a forming box measuring 256.5cm×104.1 cm, which was located on top of a metal caul plate. After thestrand mat was formed, the forming box was removed, a metal screen wasplaced on top of the mat, and the assembly was placed in a largehydraulic press. The mat was pressed to the target thickness using aninitial pressure of 750 psi (51.7 bar), a temperature of 210° C. and atotal press cycle time of 4-5 minutes. The use of metal shims aided incontrolling panel height (thickness). After cooling, the OSB panels weretrimmed to their final dimensions and conditioned, in preparation fortunnel testing. All panels were tested on the smooth side, i.e. the sidethat was in contact with the metal caul plate. Table 6a and 6b show theresults of the ASTM E2768 tunnel test.

TABLE 6a Amount of flame-retardant in core layer and surface layer andresults for example 5 Core layer Surface layer polyethylene amountpolyethylene amount amine FR-treated amine FR-treated panel phosphatestrands in phosphate APP GUP strand in thickness Sample (wt. %) wt. %(wt. %) (wt. %) (wt. %) wt. % (cm) control 0 0 0 0 0 0 1.6  40 4.8  507.5 7.5  25 1.6  41 4.8  50 7.5 7.5  25 1.6  42 6.8  70 20 10  15 1.6 43 6.8  70 20 20  15 1.6  44 15  50 15  25 1.6  45 20  50 20  25 1.6  463.4  50 15 10  25 1.12 control 0 0 0 0 0 0 1.12

Amount of FR in wt. % refers to the weight fraction of treated strandsused in the core or surface layers. For example, if FR 50 wt. % for thecore, and FR 25 wt. % for the surface layer, in this case where thereare two surface layers each having 25% of the treated strands, the totalsurface layer has 50 wt. % FR. All percentages are percentages by weightof the OSB.

TABLE 6b Results of the ASTM E2768-11 tunnel test and ASTM D1037 testfor example 5 Internal bond Ignition Total FR strength Sample FSI MFF(cm) MFF (ft) time (sec.) (wt. %) (psi) control >100 na na na 0 107 4040 518 17.0 43 9.9 41 50 732 24.0 51 9.9 42 20 488 16.0 50 13.8 43 5 30810.1 59 16.8 100 44 25 549 18.0 45 15 45 25 427 14.0 48 20 46 20 31710.4 44 14.2 120 control >100 na na na 0 125

As shown in Table 6a and 6b, it may be seen that the combination ofwater-soluble and powder flame-retardants, together with the use of agradient approach (e.g., samples 40, 41, 42 and 43 in Table 6a and 6b)exhibited a marked improvement in reducing the Flame Spread Index (FSI),Maximum Flame Front (MFF) and Ignition time according to ASTM E84 orE2768 procedures defined above. In particular, sample 43 which containedonly 16.8% total two-part flame-retardant, was able to achieve a Class Afire rating (FSI<25, MFF<320 cm).

1-11. (canceled)
 12. A flame-retardant oriented strand board comprising:at least one inner layer and at least one outer layer, wherein theoriented strand board comprises a two part flame-retardant comprising: afirst-part comprising a water-soluable flame retardant having asolubility in water of at least about 400 grams per liter (g/L) at roomtemperature that has been applied in the form of a solution, and asecond-part comprising a flame-retardant powder that has been applied inthe form of a powder, wherein the at least one inner layer comprises thewater-soluble flame-retardant, and wherein the at least one outer layercomprises the flame-retardant powder.
 13. (canceled)
 14. Theflame-retardant oriented strand board of claim 12, wherein the at leastone outer layer further comprises the water-soluble flame-retardant. 15.The flame-retardant oriented strand board of claim 12, wherein the atleast one outer layer comprises a greater total amount of the two-partflame-retardant than the at least one inner layer.
 16. Theflame-retardant oriented strand board of claim 12, wherein the orientedstrand board comprises 20 wt. % or less of the two-part flame-retardant.17. The flame-retardant oriented strand board of claim 12, wherein theoriented strand board has an internal bond strength of about 50 psi orgreater.
 18. A method of forming a flame-retardant oriented strand boardas defined in claim 12, the method comprising applying a two partflame-retardant comprising: a first-part comprising a water-solubleflame retardant having a solubility in water of at least about 400 gramsper liter (g/L) at room temperature to be applied in the form of asolution, and a second-part comprising a flame-retardant powder to beapplies in the form of a powder, wherein: an aqueous solution comprisingsaid water-soluble flame-retardant is applied to a first furnish; andthe first part comprising the water-soluble flame-retardant is appliedto a first furnish in the form of an aqueous solution; and thesecond-part comprising a flame-retardant powder is applied to a firstfurnish in the form of a flame-retardant powder; wherein thewater-soluble flame-retardant is present in the aqueous solution in anamount of 40 wt. % or greater, wherein the first furnish is configuredto form an oriented strand board without an additional drying step. 19.The method of claim 18, optionally further comprising applying thewater-soluble flame-retardant to a second furnish, wherein the firstfurnish forms the at least one outer layer and the second furnish formsat least one inner layer.
 20. The method of claim 18, wherein at leastone of the first furnish and the second furnish is formed into a mat andpressed.
 21. The method of claim 20, wherein the second furnish is aportion of the first furnish that is separated from the first furnishafter applying the aqueous solution but prior to applying theflame-retardant powder.
 22. (canceled)
 23. (canceled)